The present invention relates generally to signal quality measurement, and in particular to synchronization of a stored test signal with a received signal, the quality of which is to be measured.
In order to find weak spots of for example, a telephony system or a cellular radio communication system it is possible to transmit a known speech signal and to compare the received signal with a copy of the same signal. A problem that must be solved before the comparison may be performed is the synchronization of the samples of the stored copy with the samples of the received signal.
Citation [1] describes a transmission quality rating system, in which a test signal provided with a synchronization signal in the form of several chirp signals is repeatedly transmitted from a transmitter to a receiver. At the receiver the synchronization signal is used to find the beginning of the test signal. Thereafter the synchronization signal is discarded, and the actual test signal is used for quality rating. A drawback of this method is that the time occupied by the synchronization signal may not be used for rating, which makes the final rating less reliable. Another drawback of this prior art method is that if synchronization is lost during the test signal, for example due to a handover in a cellular radio communication system, re-synchronization is not possible until the test signal ends and a new chirp signal is transmitted, which may take as long as 20-30 seconds.
Citation [2] describes a signal synchronization method in a radio receiver, in which a dedicated synchronization sequence is combined with a known information carrying signal in order to reduce the synchronization time.
An object of the present invention is a signal quality measurement method and system that are based on a synchronization method which allows quality measurement on the entire received signal.
Briefly, the present invention achieves this object by selecting synchronization patterns from the test signal itself, and by using these patterns for both synchronization and quality measurement.
Another object of the invention is a signal quality measurement method that includes a synchronization method which allows frequent re-synchronization.
A further object of the invention is a synchronization pattern selection method for selecting suitable synchronization patterns from a test signal.
Still another object of the invention is a synchronization position refinement method.